1. Field of the Invention
The present invention pertains to a releasable or separable connector and, more particularly, to such a connector having a tensionable member severed by a pyrotechnic device.
2. Description of the Related Art
Typically a load being lowered, as by parachute with retrorocket retardation, must be released at a selected time from a tensioned element, such as a strap, supporting the load during lowering; and various releasable connector arrangements have been used for this purpose. In these arrangements a releasable connector disposed in the tensioned element is actuated from a suitable source of electrical energy at the selected time. Such a connector may be a mechanical device unlatched by a solenoid or, commonly with parachuted loads, a pyrotechnic cutter in which an electrically ignited squib provides gas pressure driving a piston-like blade into cutting relation with a supporting strap or the like.
These prior art arrangements have various deficiencies. Mechanical devices are heavy for their strength; and pyrotechnic cutters of a size to sever a single load supporting strap are expensive because they cannot be reused and, in some applications, may be dangerous because of the amount of energetic material required in a squib to sever such a single strap. Failure of a single such mechanical device or a pyrotechnic cutter would cause mission failure, but their duplication to provide redundancy would increase the problems with weight, expense, and pyrotechnic safety. In many applications of such a releasable connector, the connector must be compactly stowed together with a parachute, supporting straps, and the load so that the connector must be compact and not have any projecting portions that might be snagged during deployment. It is desirable that such a connector be usable and reusable with conventional parachute rigging links to the elements connected and released by the connector. A releasable connector subjected to relatively high temperatures, such as exhaust from a retrorocket, must not rely on materials weakened by these temperatures.
It is essential that shock loads on parachute opening or varying loads and relative movement at the connector, as might be caused by repetitive swinging of a load suspended from a parachute, not affect the load carrying capacity of the connector.
A further problem is that lines or straps under tension when such a releasable connector is in use must not become disengaged from the connector or snag connected elements due to stretching from such shock or varying loads. Stretching may be minimized by the use of materials such as extended chain polyethylene fiber or para-aramid fiber which have high tension strength and modulus of elasticity. However, the strength of extended chain polyethylene fibers decreases rapidly at temperatures above 100.degree. C. and fibers of para-aramid material are brittle so that flexible elements constructed of this material are easily damaged by chafing due to such repetitive movement. Para-aramid fibers are greatly weakened by a bend that might form on deployment or be used in attaching such a flexible element, and it is highly desirable that para-aramid elements not be knotted or even pass over a rounded edge. Another problem is that it is difficult to provide and maintain even loading of paralelled, tensioned elements that must be equally loaded to minimize weight. It is especially difficult to provide this even loading with para-aramid fiber which has a high coefficient of friction, particularly with itself, and must not be subject to chaffing when subjected to shock and repetitive loads.
For many applications, it is highly desirable that such a releasable connector be low in cost, both initially and by being reusable, and yet be low in weight and bulk while being both safe and reliable in operation. In space applications the cost and the reusability of such releasable connectors are not significant; however, it is evident that all of the other problems and deficiencies are particularly severe and that no compromises are possible between weight, bulk, safety, and reliability.